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Canadian Shield
The Canadian Shield, also called the Laurentian Plateau, or ''Bouclier Canadien'' (French), is a large area of exposed Precambrian igneous and high-grade metamorphic rocks (geological shield) that forms the ancient geological core of the North American continent (North American or Laurentia craton), covered by a thin layer of soil.〔Essentials of Geology, 3rd ed, Stephen Marshak〕 It is an area mostly composed of igneous rock which relates to its long volcanic history. It has a deep, common, joined bedrock region in Eastern and central Canada and stretches North from the Great Lakes to the Arctic Ocean, covering over half of Canada; it also extends South into the Northern reaches of the United States. Human population is sparse, and industrial development is minimal,〔(Canadian Shield ) - Columbia Encyclopedia Sixth Edition, 2005〕 while mining is very prevalent.
== Geographical extent ==
The Canadian Shield is a physiographic division, consisting of five smaller physiographic provinces, the Laurentian Upland, Kazan Region, Davis, Hudson, and James. The shield extends into the United States as the Adirondack Mountains (connected by the Frontenac Axis) and the Superior Upland. The Canadian Shield is U-shaped, but almost semi-circular, which yields an appearance of a warrior's shield, and is a subsection of the Laurentia craton signifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils. The Canadian Shield is more than 3.96 billion years old. The Canadian Shield once had jagged peaks, higher than any of today's mountains, but millions of years of erosion have changed these mountains to rolling hills.
The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic Eon that were progressively amalgamated during the interval 2.45 to 1.24 Ga, with the most substantial growth period occurring during the Trans-Hudson orogeny, between ca. 1.90 to 1.80 Ga. The Canadian Shield was the first part of North America to be permanently elevated above sea level and has remained almost wholly untouched by successive encroachments of the sea upon the continent. It is the Earth's greatest area of exposed Archean rock. The metamorphic base rocks are mostly from the Precambrian Supereon (between 4.5 billion and 540 million years ago), and have been repeatedly uplifted and eroded. Today it consists largely of an area of low relief above sea level with a few monadnocks and low mountain ranges (including the Torngat and Laurentian Mountains) probably eroded from the plateau during the Cenozoic Era. During the Pleistocene Epoch, continental ice sheets depressed the land surface (see Hudson Bay), scooped out thousands of lake basins, and carried away much of the region's soil.
When the Greenland section is included, the Shield is approximately circular, bounded on the northeast by the northeast edge of Greenland, with Hudson Bay in the middle. It covers much of Greenland, Labrador, most of Quebec north of the St. Lawrence River, much of Ontario including northern sections of the southern peninsula between the Great Lakes, the Adirondack Mountains〔Peterson Field Guide to Geology of Eastern North America by Roberts, David & Roger Tory Peterson.〕 of nowhere close to New York, the northernmost part of Lower Michigan and all of Upper Michigan, northern Wisconsin, northeastern Minnesota, the central/northern portions of Manitoba away from Hudson Bay, northern Saskatchewan, a small portion of northeastern Alberta,〔(Alberta Heritage - Alberta Online Encyclopedia ) - The Canadian Shield Region of Alberta〕 and the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border (Northwest Territories and Nunavut). In total, it covers approximately . It covers even more area and stretches to the Western Cordillera in the west and Appalachians in the east, but the formations are still underground. The underlying rock structure does include Hudson Bay and the submerged area between North America and Greenland.
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